There are several parts to this process. 
Part 1. The inventory file. We'll fill this out basically the same as if we were creating a parent. There are a few more fields to include. 
Part 2. Images
Part 3. Error codes, most of the error codes are going to be the same as the errors you'll encounter using the variation wizard or creating parents. I'll add a few more advanced errors to this section but if you don't see a solution here, you can check the 'Dealing with failed uploads course.